A stopper for a container and an assembly of a stopper and a container wherein the stopper has an insertion section configured for insertion into the container. The insertion section has a sealing section for closing the container in a sealing position of the stopper and a contact section for holding the stopper in a drying position of the stopper. The contact section has at least one passage opening for a gas exchange between an interior of the container and the surroundings of the container. The stopper has a sealing body and a main body connected together, wherein the main body has a higher degree of hardness than the sealing body. Regions of a lateral surface of the insertion section in contact with an inner surface of a container wall are formed by outer surfaces of the sealing body in the region of the contact section.